Powder metallurgy sputtering targets and methods of producing same

ABSTRACT

A method of forming a sputtering target and other metal articles having controlled oxygen and nitrogen content levels and the articles so formed are described. The method includes surface-nitriding a deoxidized metal powder and further includes consolidating the powder by a powder metallurgy technique. Preferred metal powders include, but are not limited to, valve metals, including tantalum, niobium, and alloys thereof.

This application is a divisional of U.S. patent application Ser. No.11/431,259, filed May 10, 2006 (now U.S. Pat. No. 7,601,296), which is adivisional of U.S. patent application Ser. No. 10/752,270, filed Jan. 6,2004 (now U.S. Pat. No. 7,067,197), which claims priority to U.S.Provisional Patent Application No. 60/438,465, filed Jan. 7, 2003, andincorporated in their entirety by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to sputtering targets and other metalarticles as well as methods of making the same. More particularly, thepresent invention relates to methods for forming powder metallurgysputtering targets and other metallurgical articles made from valvemetal materials.

Sputtering targets are used for many purposes, including producing thinfilms of metals or compounds. In a sputtering process, a source materialis bombarded with plasma ions that dislodge or eject atoms from thesurface of a sputter target. The ejected atoms are deposited atop asubstrate to form a film coating that is typically several atomic layersthick.

Sputtering targets can be made from valve metal materials. Valve metalsgenerally include tantalum, niobium, and alloys thereof, and also mayinclude metals of Groups IVB, VB, and VIB and alloys thereof. Valvemetals are described, for example, by Diggle, in “Oxides and OxideFilms”, Vol. 1, pages 94-95, 1972, Marcel Dekker, Inc., New York,incorporated in its entirety by reference herein.

Semiconductor technology is forecast to be the largest market fortantalum sputtering targets. Semiconductors are the building blocks of aclass of microelectronic devices that include microprocessors found inmainframe computers, work stations, and PCs, digital signal processorsfor cell phones and telecommunication equipment, andapplication-specific integrated circuits used in digital organizers,cameras, and electronic appliances.

Driven by continuous reductions in costs, device size, and improvedperformance, copper is replacing aluminum for use as interconnects innext generation semiconductors. To prevent the copper of theinterconnects from migrating through the semiconductor device and“poisoning” the transistors and other electronics, a diffusion barrieris commonly interposed between the interconnects and the device.Tantalum (Ta) and tantalum nitride (TaN), which is typically produced bythe reactive sputtering of a tantalum target in the presence ofnitrogen, are commonly-used barrier materials for copper interconnects.By way of example, microprocessors operating at clock speeds in excessof 1000 MHz, such as AMD's Althon and Intel's Pentium 4, as well asIBM's I STAR and P-750 processors found in modern mainframe systems,each use copper interconnects along with a tantalum diffusion barrierlayer.

Films having uniform chemistry and thickness are preferred for diffusionbarrier applications. To obtain uniform chemistry and thickness, it ispreferable to sputter a target having certain desirable properties,including, high purity, a fine grain size, and a homogeneous texturevoid of strong (001) texture bands. Commonly, tantalum materialsproduced from ingot metallurgy (ingot-met) techniques as described, forexample, in U.S. Pat. No. 6,348,113 (Michaluk et al.), which isincorporated in its entirety by reference herein, are specified forsputtering applications. Ingot-met tantalum material may produce thepurity levels and maximum grain size desirable for diffusion barrierapplications. However, by nature, it is difficult to refine and controlthe grain size and texture homogeneity in high purity, unalloyed andundoped metallic materials. As such, the minimum average recrystallizedgrain size attainable in wrought high purity ingot-met tantalum targetsmay be about 10 microns. In addition, ingot-met tantalum targets mayalso exhibit textural banding and consequently may produce sputteredfilms of highly variable thicknesses.

Powder metallurgy (powder-met) techniques offer an alternative method ofmanufacturing tantalum material and tantalum sputtering targets. Properprocessing can produce powder-met tantalum sputtering targets having afiner grain size than that attainable in ingot-met tantalum targets. Thehigher amounts of interstitial impurities inherent in the powder-metmaterials increases the work hardening rate, and hence the rate of newdislocation line length generation and subsequent recrystallizationresponse during annealing, by behaving like a dispersion of fineparticles within the matrix. For this reason, a smaller, morehomogeneous grain structure is achieved in commercially producedpowder-met tantalum thin gauge strip and wire than that which isattainable in ingot-met tantalum products of similar gauge.

The (isostatic) consolidation of metal powders is a viable andestablished means of producing certain metal articles having a randomand homogeneous texture. The combination of fine grain size having arandom distribution of crystal orientations promote the uniformity ofwork (e.g., homogeneous strain hardending of all grains) duringsubsequent deformation processing of powder-met tantalum sputteringtargets, thus avoiding the formation of sharp texture bands inpowder-met sputtering targets. The powder-met tantalum sputteringtargets are expected to deposit films having exceptional thicknessuniformity.

Commercially available tantalum powder, however, contains unacceptablyhigh levels of oxygen for use in diffusion barrier applications. Underambient conditions, tantalum metal has a passive coating, e.g., such asapproximately 1 nm or less to 3 nm or more thick oxide film that iscomprised of tantalum oxide and absorbed oxygen gas (L. A. Rozenberg andS. V. Shtel'makl, “State of Oxygen in Tantalum Powders,” IvestiyaAkademii Naut SSSR. Metally, (4) 1985, pp. 163, incorporated in itsentirety by reference herein). Commercial tantalum powder that isdeoxidized and then exposed to oxygen to reform a passive oxide coatingwill still typically contain more than 100 ppm oxygen. Preferably, theoxygen content of tantalum sputtering targets is limited to 100 ppm orless. Excessive oxygen in the sputtering target can lead to the creationof tantalum-oxide within the deposited tantalum nitride barrier layerand a subsequent undesirable increase in the RC delay in theinterconnect line.

Accordingly, methods for forming low-oxygen metal powder, and sputteringtargets or other metal articles produced from the metal powder, areneeded for depositing high-integrity films via reactive sputtering.

SUMMARY OF THE PRESENT INVENTION

It is therefore a feature of the present invention to provide a methodto form a powder metallurgy sputtering target and other metal articleshaving low oxygen content.

Another feature of the present invention is to provide a method ofdeoxidizing tantalum and surface-nitriding a metal powder by passivatingthe deoxidized powder in the presence of nitrogen.

Another feature of the present invention is forming metallurgicalarticles from surface-nitrided metal powders having low oxygen content.

Another feature of the present invention is to provide a sputteringtarget assembly having a consolidated surface-nitrided metal powdersputtering target and a backing plate.

Another feature of the present invention is to provide a sputteringtarget having an average grain size of about 100 microns or less.

Another feature of the present invention is to provide a sputteringtarget having a random texture.

Another feature of the present invention is to perform thermomechanicalprocessing on a metal article formed from metal powder to produce asputtering target having an average grain size of about 100 microns orless and a texture that lies on or near the (111)-(100) symmetry line ofthe Maxwell standard orientation triangle.

Additional features and advantages of the present invention will be setforth in part in the description that follows, and in part will beapparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and attained by means of the elements andcombinations particularly pointed out in the description and appendedclaims.

To achieve these and other advantages, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention relates to a method of forming asputtering target or other metal article. The method includessurface-nitriding a deoxidized metal powder. The method can involveconsolidating the surface-nitrided metal powder by a powder metallurgytechnique. The metal powder can optionally be consolidated into asputtering target and further machined or processed by conventionalprocessing techniques.

The present invention further relates to a formed metallurgical articlehaving an oxygen content of about 100 ppm or less and a nitrogen contentof at least about 10 ppm.

The present invention also relates to providing a surface-nitrided metalpowder having a tantalum nitride shell.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention, as claimed.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention is directed to providing a metal powder,preferably a valve metal powder, having an oxygen content of 300 partsper million (ppm) or less, and more preferably 100 ppm or less, and anitrogen content of at least 10 ppm, and more preferably at least 40ppm. Preferably, the valve metal powder is tantalum, niobium, or alloysthereof. The present invention further relates to a method for formingsputtering targets and other metal articles from a surface-nitrided,low-oxygen metal powder. Other metal articles include, but are notlimited to, capacitors, anodes, capacitor cans, and wrought products.The present invention further relates to the metal films produced bysputtering targets and other deposition source materials manufacturedfrom surface-nitrided, low oxygen metal powders.

In more detail, the present invention relates to valve metal powdershaving nitrogen contained therein. The amount of nitrogen present isgenerally greater than nitrogen amounts found in valve metal powders asimpurities. The majority of the nitrogen present in the valve metalpowders of the present invention is a result of intentional conditionswhich lead to increased levels of nitrogen on the surface of the valvemetal powders (i.e., surface-nitriding of the valve metal). The nitrogenpresent in the valve metal can be accomplished in any manner. Forinstance, the nitrogen can be introduced (e.g., doped) into the valvemetal during any processing stage of the valve metal, such as during oneor more of the following stages: deoxidation; hydriding of the valvemetal; delubing of the valve metal; any sintering of the valve metal(e.g., such as sintering of the valve metal capacitor anode); anythermal processing of the valve metal; any heat treatment stage; oranytime before or after any one or more of these processing steps orstages.

Any means can be used to surface-nitride the valve metal material, suchas, but not limited to, exposure to nitrogen containing environments(e.g., N₂ and NH₃ gases) or nitrogen-containing materials, preferablyduring a thermal cycling to defuse the nitrogen into the material (e.g.,preparing a solid-solution of nitrogen by reaction of nitrogencontaining materials by diffusion from direct physical contact or gasadsorption and/or absorption).

The valve metal that can be used in this embodiment is any valve metalpowder, such as flaked, angular, nodular, and mixtures or variationsthereof. With respect to the flaked valve metal powder, the valve metalpowder can be characterized as flat, plate shaped, and/or platelet. Anyof the embodiments set forth and/or described below can also besubjected to conditions that will lead to valve metal powders having thedescribed nitrogen amounts. Examples of valve metal powders includethose having mesh sizes of from between about 40 to about 400 mesh orless, and preferably, of from between about 40 to about 100 mesh. TheBET surface area of the valve metal powder can be from about 0.1 m²/g toabout 10 m²/g or greater. The BET can be less than about 10 m²/g, or canbe less than about 1 m²/g, or can be less than about 0.1 m²/g.

One method to deoxidize valve metal powders, such as tantalum powder, isto mix alkaline earth metals, magnesium, aluminum, yttrium, carbon, ortantalum carbide with the tantalum powder. The alkaline earth metals,aluminum, and yttrium may form refractory oxides that are preferablyremoved, such as by acid leaching, before the material can be used toproduce capacitors. Typically, the post-deoxidation acid leaching isperformed using a strong mineral acid solution including, for example,hydrofluoric acid, at elevated temperatures of up to about 100° C. ormore to dissolve the refractory oxide contaminants. Also, cold acidleaching can be used, preferably after deox to lower oxygen levels in Tapowder or other metal powders. Other methods have been proposed,including using a thiocyanate treatment, or a reducing atmospherethroughout the tantalum powder processing, to prevent oxidation andprovide low oxygen content.

Other processes for controlling the oxygen content of valve metalmaterials, such as tantalum, niobium, and their alloys, include the useof getter materials. For example, U.S. Pat. No. 4,722,756 (Hard), whichis incorporated in its entirety by reference herein, describes heatingthe materials in an atmosphere containing hydrogen gas in the presenceof a metal, such as zirconium or titanium that is more oxygen activethan tantalum or niobium. Another process for controlling the oxygencontent of valve metal materials is disclosed in U.S. Pat. No. 4,964,906(Fife), which is incorporated in its entirety by reference herein. Theprocess involves heating a tantalum material or other metal in ahydrogen-containing atmosphere in the presence of a getter materialhaving an oxygen concentration lower than the valve metal material.

The method of the present invention includes surface-nitridingdeoxidized metal powder to form a metal powder having an oxygen content,preferably, of about 300 ppm or less and having a nitrogen content,preferably, of at least about 10 ppm. The surface-nitrided metal powdercan be consolidated by a powder metallurgy technique to form asputtering target or other metallurgical article. The method canoptionally include further processing the sputtering target or othermetallurgical article using conventional thermomechanical processingsuch as forging and rolling, and finishing techniques such as machining,polishing, and surface conditioning.

In one embodiment of the present invention, a deoxidized metal powderand a nitrogen gas (e.g., N₂ or NH₃) or other nitrogen source arecontacted to form a surface-nitrided metal powder having an oxygencontent from about 300 to about 100 ppm or less and having a nitrogencontent of at least from about 10 to about 40 ppm or higher. Contactingcan be by any conventional method, including doping the metal powderwith the nitrogen gas, introducing the gas to the metal powder, reactingthe gas and the metal powder, absorption of the gas by the metal powder,or one of the methods described earlier, or any combination thereof.Contacting the metal powder and the nitrogen gas can be under vacuum,under a pressure (positive, negative, or neutral) of an inert gas, orboth. Contacting can be in any suitable container, for example, in aretort, furnace, or vacuum chamber. The container containing the metalpowder and the nitrogen gas can be backfilled with an inert gas. Anyinert gas can be used, such as argon. The container can be vacuumed to adesired pressure and the container backfilled with nitrogen. The amountof nitrogen used to backfill can be calculated based on the amount ofthe metal powder and a desired nitrogen concentration of the metalpowder formed. The temperature in the container can be increased topromote contacting or absorption of the metal powder and the nitrogen.

The metal powder can be nitrogen-passivated or surface-nitrided in theprocess described above. Surface-nitriding the metal powder can have theeffect of reducing the pyrophorisity of the metal powder. The process ofsurface-nitriding the metal powder can produce a metal powder having anitride shell. For example, surface-nitrided tantalum and niobiumpowders can have tantalum nitride and niobium nitride shells,respectively. Surface-nitriding the metal powder according to thepresent invention may have the effect of inhibiting the re-absorption ofoxygen by the deoxidized metal powder. The surface-nitrided metal powdercan have an oxygen content of about 300 ppm or less, and preferably,from about 100 ppm to about 5 ppm or about 1 ppm or less. Thesurface-nitrided metal powder can have a nitrogen content of at leastabout 10 ppm, and preferably, at least about 40 ppm, such as from about10 ppm to about 10,000 ppm or more (e.g. from about 10 ppm to about300,000 ppm). Other ranges include less than about 100 ppm, from about100 ppm to about 500 ppm, from about 500 ppm to about 1000 ppm, andgreater than about 1000 ppm. The surface-nitrided metal powderpreferably has a particle diameter of about 200 microns or less to avoidarcing in the sputtering process, and preferably 100 microns or less tofacilitate consolidation and subsequent thermomechanical processing.

According to the present invention, a formed metallurgical articleincluding a sputtering target, having an oxygen content below about 100ppm and a nitrogen content of at least about 40 ppm, can be producedfrom metal powder, preferably tantalum, niobium or alloy, having anoxygen content below about 100 ppm and a nitrogen content of at leastabout 40 ppm, by any powder metallurgy technique, used, for example, fortantalum, niobium and their alloys. In one embodiment, the metal is notexposed to a temperature greater than about 0.7 T_(H). For purposes ofthe present invention, the homogolous temperature is the ratio of theabsolute temperature of a material to its absolute melting temperature,and is expressed as, T_(H)=T/T_(m). Exemplary of the powder metallurgytechniques used for forming the metal products are the following, inwhich the steps are listed in order of performance. Any of thetechniques can be used in the present invention, and preferably, anysintering, heating, or other handling, of the metal does not expose themetal to a temperature greater than 0.7 T_(H):

1. Cold Isostatic Pressing, Sintering, Encapsulating, Hot IsostaticPressing and Thermo-Mechanical Processing;

2. Cold Isostatic Pressing, Sintering, Hot Isostatic Pressing andThermo-Mechanical Processing;

3. Cold Isostatic Pressing, Encapsulating, Hot Isostatic Pressing andThermo-Mechanical Processing;

4. Cold Isostatic Pressing, Encapsulating and Hot Isostatic Pressing;

5. Encapsulating and Hot Isostatic Pressing;

6. Cold Isostatic Pressing, Sintering, Encapsulating, Extruding andThermo-Mechanical Processing;

7. Cold Isostatic Pressing, Sintering, Extruding, and Thermo-MechanicalProcessing;

8. Cold Isostatic Pressing, Sintering, and Extruding;

9. Cold Isostatic Pressing, Encapsulating, Extruding andThermo-Mechanical Processing;

10. Cold Isostatic Pressing, Encapsulating and Extruding;

11. Encapsulating and Extruding;

12. Mechanical Pressing, Sintering and Extruding;

13. Cold Isostatic Pressing, Sintering, Encapsulating, Forging andThermo-Mechanical Processing.

14. Cold Isostatic Pressing, Encapsulating, Forging andThermo-Mechanical Processing;

15. Cold Isostatic Pressing, Encapsulating and Forging;

16. Cold Isostatic Pressing, Sintering, and Forging;

17. Cold Isostatic Pressing, Sintering and Rolling;

18. Encapsulating and Forging;

19. Encapsulating and Rolling;

20. Cold Isostatic Pressing, Sintering and Thermo-Mechanical Processing;

21. Spray Depositing;

22. Mechanical Pressing and Sintering; and

23. Mechanical Pressing, Sintering, Repressing and Resintering.

Other combinations of consolidating, heating and deforming may also beused. Examples of powder-met techniques are described, for example, inU.S. Pat. No. 5,580,516 (Kumar), incorporated in its entirety byreference herein.

Other processes that expose the metal powder to processing temperaturesabove 0.7 T_(H) can be utilized to fabricate or consolidate the metalpowder, or both. For example, the metal powder can be produced by firstcasting a metal ingot, hydriding the cast ingot, crushing the hydridedmetal ingot, then optionally removing the hydrogen from the resultantmetal powder. In another example, the metal is melted then atomized byprocesses including, but not limited to, gas atomization (includingnitrogen gas atomization), water atomization, and rotating electrodepowder processes. The powders can be subsequently deoxidized thensurface-nitrided using a process such as that described below. Thesurface-nitrided metal powder can then be consolidated by pressing andsintering in vacuum at a temperature above 0.7 T_(H) to produce ahigh-density metal compact.

In one embodiment of the present invention, a starting metal material,preferably a valve metal including, tantalum, niobium, or alloy powder,such as one produced by a sodium reduction process, is placed into acontainer such as a vacuum chamber, with a getter material. An exampleof a sodium reduction process for producing tantalum powder isdescribed, for example, in U.S. Pat. No. 6,348,113. The getter materialcan be any material having a higher affinity for oxygen than the powder,i.e., an oxygen getter, and is preferably an active metal. One metalthat is more oxygen active than the powder, is magnesium. Preferably,the starting metal material or compound has an oxygen content less thanabout 1000 ppm.

A vacuum can be drawn in the chamber. The chamber can be backfilled withan inert gas, preferably argon. The chamber is heated to a desiredtemperature. For instance, the chamber can be heated to a temperaturebelow the melting temperature and preferably to a homologous temperature(T_(H)) of about 0.7 T_(H), or less, for example, in the range of about550 to about 1150° C. of the metal powder. The heating is continued fora time sufficient to allow oxygen to diffuse out of the metal powder,for example, preferably about 60 minutes. A vacuum can again be drawn inthe chamber and the chamber backfilled with an inert gas, such as argon.The chamber can then be cooled or allowed to cool to a desiredtemperature, about 300° C., for instance. When the temperature in thechamber is at about the desired temperature, a vacuum can be drawn inthe chamber to a desired pressure, for example, about 50 torr.

The metal powder is then contacted with nitrogen. The chamber can bebackfilled with nitrogen. The amount of nitrogen to be used isdetermined based upon the amount of metal powder in the chamber and thedesired nitrogen concentration of the formed metal powder. The chambercan be heated to a desired temperature and/or at a desired rate, e.g.,preferably about 1° C. per minute, causing the nitrogen to react with orbe absorbed by the metal powder. The chamber can be backfilled with aninert gas, such as argon. The residual getter material, containing theoxygen, is removed from the metal powder, for example by selectivechemical leaching or dissolution of the powder. According to oneembodiment, the surface-nitrided metal powder produced by the methoddescribed above, can be consolidated to form a metal or metallurgicalarticle. Consolidating can be by a powder-met technique, for example, asdescribed above.

As described above, in the process for producing formed powder metalarticles of tantalum, niobium and their alloys, a tantalum, niobium, oralloy of tantalum or niobium, powder is, if needed, deoxidized, to anoxygen content of less than about 300 ppm, and preferably of less thanabout 100 ppm, preferably without exposing the metal powder to atemperature greater than about 0.7 T_(H), and the powder issurface-nitrided, to have a nitrogen content of at least about 10 ppm,and preferably, of at least about 40 ppm, and then is consolidated toform a tantalum, niobium, or alloy metallurgical article, having anoxygen content below about 300 ppm, preferably below about 100 ppm, andhaving a nitrogen content of at least about 10 ppm, and preferably of atleast about 40 ppm.

The metallurgical article described above is preferably a sputteringtarget assembly including two components, namely, a backing plate and asputter target. The sputter target and the backing plate can be anysuitable target grade and backing plate grade materials. The powder usedto make the metallurgical article such as the sputtering target as wellas the resulting metallurgical article, such as the sputter target canhave any purity with respect to the metal. For instance, the purity canbe 99% or greater such as from about 99.5% or greater and morepreferably 99.95% or greater and even more preferably 99.99% or greater.The metallurgical article such as a sputter target can have any suitablegrain size and/or texture. For instance, the article can have an averagegrain size of about 300 microns or less and more preferably an averagegrain size of 100 microns or less and even more preferably a grain sizeof about 50 microns or less and most preferably an average grain size ofabout 10 microns. Suitable ranges include from about 10 microns to about100 microns in average grain size.

In addition, the texture can be random, such that the grains comprisingthe metal article exhibit minimal or no preferred crystallographicorientation. Or, the metal article can be thermomechanically processedto produce a preferred orientation that lies along or near the(111)-(100) symmetry line of the Maxwell standard orientation triangle.Examples of preferred orientations include a primary (111) texture or aprimary (100) texture that can be on the surface or throughout theentire thickness of the metal article. Preferably, the texture isuniform. Also, the article can have a mixed (111):(110) texturethroughout the surface or throughout the entire thickness of the metalarticle. In addition, the metal article can be substantially void oftextural banding, such as substantially void of (100) textural banding.In addition, the metal article can be drawn, stretched, or extruded toproduce a (110) texture. The (110) crystal planes in Body Center Cubic(BCC) metals have the highest areal density of atoms, and sputteringtargets having a (110) have the highest sputtering yield compared tosputtering targets having other primary orientations.

With respect to the target materials to be used in the method of thepresent invention, examples include, but are not limited to, tantalum,niobium, cobalt, titanium, copper, aluminum, and alloys thereof, forinstance, the alloys described above. Examples of the backing plateinclude, but are not limited to, copper, or a copper alloy, tantalum,niobium, cobalt, titanium, aluminum, and alloys thereof, such as TaW,NbW, TaZr, NbZr, TaNb, NbTa, TaTi, NbTi, TaMo, NbMo, and the like. Nolimitation exists as to the type of materials used in the sputteringtarget and the backing plate. The thicknesses of the backing and thetarget material can be any suitable thickness used for formingsputtering targets. Alternatively, the backing plate and the targetmaterial or other metal plate to be bonded onto the backing plate can beany suitable thickness for the desired application. Examples of suitablethicknesses of the backing plate and of the target material include, butare not limited to, a backing plate with a thickness of from about 0.25or less to about 2 inches or more in thickness and targets with athickness ranging from about 0.06 inches to about 1 inch or greater. Thesputtering target can also have an interlayer as is conventional in theindustry. Furthermore, the sputtering target can be a hollow cathodemagnetron sputtering target and can be other forms of sputteringtargets. Except as mentioned above, the purity, texture, and/or grainsize and other properties, including size and the like are not criticalto the present invention. The present invention provides a method ofmaking a powder-met sputtering target assembly with any type of sputtertarget and backing plate.

In one embodiment of the present invention, consolidating comprisescompressing said surface-nitrided metal powder to about 80 to about 100%of theoretical density with compressive forces of from about 30,000 toabout 90,000 psi. In another embodiment, the sputtering target of thepresent invention has a yield strength from about 18,000 to about 40,000psi and an elongation to failure of greater than 20% when tested intension at a strain rate of 0.005 inches/inch per minute for a standardASTM E8 subscale tensile tested in accordance to ASTM E8.

As noted, TaN thin films used as a diffusion barrier for copperinterconnects in high-speed microprocessors, are commonly deposited byreactive sputtering of tantalum in the presence of nitrogen. Thesputtering target according to the present invention is particularlyadvantageous for use in nitride film sputter applications, given thenitrogen content level attained in the sputtering target formed. Becausemuch of the nitrogen present in metal powder is removed by evaporationat temperatures reached in metal ingot formation, the nitrogen contentin ingot-met sputtering targets is substantially less than that in thesputtering target formed according to the present invention.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

1. A method for forming a surface-nitrided metal powder, comprising:heating a metal powder in the presence of a getter material having anaffinity for oxygen that is higher than that of said metal powder;removing said getter material from said metal powder; andsurface-nitriding said metal powder to form a surface-nitrided metalpowder having an oxygen content of about 300 ppm or less and having anitrogen content of at least about 100 ppm, wherein removing said gettermaterial occurs before, after, or concurrently with saidsurface-nitriding, and consolidating said surface-nitrided metal powderby a powder metallurgy technique to form a metallurgical article,wherein said metallurgical article is a sputter target.
 2. The method ofclaim 1, wherein said heating is at a temperature not exceeding 0.7T_(H) of said metal powder.
 3. The method of claim 1, wherein saidconsolidating is at a temperature of about 0.7 T_(H) or more of saidmetal powder.
 4. The method of claim 1, wherein said heating is at atemperature not exceeding 0.7 T_(H) of said metal powder.
 5. The methodof claim 1, wherein said heating is performed under vacuum or under aninert gas.
 6. The method of claim 1, wherein said getter materialcomprises magnesium.
 7. The method of claim 1, wherein said gettermaterial is removed by evaporation and by chemical leaching.
 8. Themethod of claim 1, wherein said surface-nitriding comprises contactingwith a nitrogen gas.
 9. The method of claim 1, wherein said metal powderfor said surface-nitriding is valve metal powder having a mesh size offrom between about 40 mesh to about 400 mesh.
 10. The method of claim 1,wherein said metal powder for said surface-nitriding is valve metalpowder having a mesh size of from between about 40 mesh to about 100mesh.